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WATER SOLUTIONS

One solution is a homogeneous mixture of two or more substances, whose relative proportions may vary within certain limits.

component of a .- The substances are components of a solution: 1 .-

SOLUTE .- It is the least abundant component of a solution. 2 .-
SOLVENT .- It is the most abundant component in the solution.

components of a solution can be found in any physical state.

When the solvent is water solution, the aqueous solution is called, if it is alcohol, alcoholic solution, etc.

When a molecular substance dissolved in water, the solute divided until individual molecules and molecular solution is called, which is characterized by poor conductor of electricity, but if an ionic compound dissolves in water, the solute divided to obtain positive and negative ions and ionic solution is called and is known for being a good conductor electricity.

CONCENTRATION OF SOLUTION .- If a solution exists the amount of solute is small, says the solution is diluted and concentrated, when the amount of solute is large. When not be given temperature most solute disband resolution was says we are face a resolution if saturated also have excess solute asserts that settlement is supersaturated.

The term concentration of a solution we use, often to refer to the description of the composition of a solution, ie to express the amount of solute that exists in a given amount solution.

METHODS FOR EXPRESSING THE CONCENTRATION OF A SOLUTION .- To express the concentration of a solution we can use physical units and chemical units.

1 .- PHYSICAL UNITS .- Among others we have:

a) PARTS PER MILLION (ppm) .- Is the concentration and the number of milligrams of solute per liter of solution.

.- Example water containing 0.05 ppm of Pb +2 is considered unfit for human consumption. This solution contains 0.05 mg of Pb +2 per liter of water.

b) WT percentage .- O solutions are those in which the composition of a solution is expressed in terms of weight of solute per 100 parts by weight of solution.

Example .- A 15% solution by weight of sodium chloride has the following composition: 15 g sodium chloride in 100 g of solution.

LARO TERM MEMORY BUILDING (45)

1. How many grams of 15% solution of NaCl is needed to extract 38g of sodium chloride by evaporating the water? 253G .- Rpta
2. many grams of concentrated hydrochloric acid having a concentration of 37.9% HCl by weight are required to have 5g of pure HCl. Rpta .- 13.2 g
3. 250g need to be prepared solution of Na (OH) to 19.7% by weight. How many grams of Na (OH) and water are needed? Rpta .- 49.25 and 200.75 g
4. What is the percentage concentration of the solution containing 85g of H2SO4 in 500 g of solution? .- 16% Rpta
5. How much water should be diluted 40g of nitric acid to obtain a 5% by weight of the substance? 760g .- Rpta
6. Calculate the volume occupied by 100g of solution Na (OH) with a density of 1.20 g / cc. Rpta .- 83.3 ml.
7. Calculate the weight of pure hydrochloric acid which exists in 5ml of hydrochloric acid with a concentration of 37.23% of weight and density of 1.19 g / cc. Rpta .- 2.22 g
8. Calculate the volume of concentrated H2SO4, 98% by weight and density of 1.84 g / cc which contains 40g of pure acid. 22.17 .- cc Rpta
9. What volume of nitric acid, HNO3, diluted density 1.11 g / cc and 19% HNO3 by weight containing 10 g of the pure substance? Rpta .- 47ml.

2 .- CHEMICAL UNITS .- These include:

a) .- MOLAR (M) The molarity of a solution is determined by the number of moles (n) solute that exist in each liter of solution.

Example .- A solution of 2 Molar concentration (2M) has the following composition: 2 moles of solute in each liter of solution.

We all know that to determine the number of moles of solute existing in a certain number of grams of a substance you can use the following formula:

If we replace n in the formula (1) this expression yields the following formula allows us calculations of molar solutions.

BUILDING LONG-TERM MEMORY (46)

1. What is the molarity of the solution containing 250mg of CaCl2 in 1500ml of solution? Rpta .- 1.5 M
2. What weight hydroxide Calcium is required to prepare 2.5 liters of solution 1.2 mole of that substance? 222g .- Rpta
3. What weight of solute are in 800 ml of 0.5 molar solution of HNO3? Rpta .- 25.2 g
4. What is the molar concentration of the solution containing 10g of HCl in 50 ml of solution? 5.5 .- M Rpta
5. What volume of 0.75 M solution could be prepared with 500 g of Na2SO4? 4.61 Rpta .- l. 6 .- Find the molarity of the solution containing 196g of H2SO4 in 500 ml of solution. Rpta .- 4 mol / l
6. How many grams of potassium permanganate, KMnO4, is needed to prepare 500ml of solution 2 M of that substance? 158g .- Rpta
7. How many grams of NaCl are in 250 ml of 2.5 molar solution? 36.56g Rpta .-
8. What is the molarity of the solution that has 100 mg in 10 ml HNO3 solution? Rpta .- 0.12 M.
9. What is the molar concentration of the solution containing 12 mmol of HI in 100 ml of solution? 0.12 M Rpta .-
10. How many milliliters of HCl, whose concentration is 38% and a density of 1.19 g / ml, are required to prepare 2 liters of 0.3 molar solution?

b) NORMAL .- (N) The normality of a solution is determined by the number of gram equivalents of solute that exist in each liter of solution.

Example: If a solution has a concentration of 0.7 normal (0.7 N) has the following composition: Contains 0.7 eq-g of solute in each liter of solution.

all know that to determine The number of eq-g of solute existing in a certain number of grams of a substance you can use the following formula:

If we replace # Eq-g in the formula (2) by this expression, we obtain formula that allows us to perform calculations on standard solutions.

c) Molality .- (m) The molality of a solution is determined by the number of moles of solute that exists in every kilogram of solvent.

Example: If a solution is 2.5 molal concentration is that it has the following composition: It contains 2.5 moles of solute per kilogram of solvent.

BUILDING LONG-TERM MEMORY (47)

1. normal concentration What is the solution that contains 10.5 g of H2SO4 in 1.5 liters of solution? Rpta .- 0.14 N
2. A solution containing 50 mg of FeCl3 in 0.5 liters of solution. What is your normal? Rpta .- 0.0015 N
3. Find the normal concentration of the solution containing 450g of NaOH in 2 liters of solution. Rpta .- 5.6 N
4. How many grams of Ca (OH) 2 must be added to water to make 3 liters of 0.1 N? Rpta .- 11.1 g
5. Calculate the number of gram equivalents of Na2CO3 to be dissolved to prepare 250 ml of solution 0.08 N. Rpta .- 0.02 eq-g
6. How many cm3 of H2SO4, 96% purity and a density of 1.8 g / cc, is required to prepare 400 ml of 0.1 N? Rpta .-
7. What is the normality of the solution of H2SO4 to 98% by weight with a density of 1.8 g / cc? Rpta .-
8. We prepare
   17.31 ml of 0.692 N for utiulizarla KMnO4 in a reaction which passes MnO4-Mn2 +. How many grams of KMnO4 are required? Rpta .- 0.379 g.

dilute solution .- Sometimes, in the laboratory, diluted solutions of known concentration with a number, also known, distilled water or mixed solutions of known concentration, need to know the concentration of the resulting solution. Below we present, by problems solved, how to perform these calculations using the following formulas. Formulas

calculations on the dissolution of solutions

Formula for calculations on mixing solutions of known concentration

BUILDING LONG-TERM MEMORY (48)

1. Calculate the volume of water to be added to 250 ml of 1.25 N to make 0.5 N Rpta .- 375 ml.
2. What volumes of 12N HCl and 3 N should be mixed to give 1 liter of HCl 6N? Rpta .- 1 / 3 L 12N, 2 / 3 L 3N
3. What volume of water should be added to 400 g of 80% ethyl alcohol to decrease to 20%? Rpta .- 1200g.
4. 150ml There is a 0.3 M solution of sulfuric acid, if you add 20ml of water, what is the molarity of the new solution? Rpta .- 0.27 mol / L